Process for the removal of cadmium ions from phosphoric acid resulting from a wet process

Abstract

A process for the removal of cadmium ions by liquid-liquid extraction from wet process phosphoric acid, which had been obtained from crude phosphate ores by dissolution with sulfuric acid, uses salts of long chain alkyl amines or ammonium bases with the chlorocomplexes of polyvalent metal ions, which are dissolved in an inert organic solvent.

We claim: 
     
       1. A process for the removal of cadmium ions from wet process phosphoric acid by liquid-liquid extraction, comprising contacting the wet process phosphoric acid with at least one salt present in an organic solvent, where the organic solvent is immiscible with water, aqueous salt solutions, and aqueous acids, and wherein the salt is selected from salts of organic primary, secondary, and tertiary amines and quaternary ammonium salts; and   separating the organic solvent phase, containing the extracted cadmium ions, from the wet process phosphoric acid;   said amine and ammonium salts, respectively, being salts which, as anions, contain chlorocomplexes of one or several polyvalent metals different from cadmium.   
     
     
       2. The process of claim 1, further comprising reextracting the extracted cadmium ions from the isolated organic phase with an acidic aqueous solution. 
     
     
       3. The process of claim 2, further comprising subsequent processing of the resulting acidic aqueous reextract solution enriched in cadmium ions. 
     
     
       4. The process according to claim 2, wherein the acidic aqueous solution used for reextraction contains anionic chlorocomplexes of one or several polyvalent metals different from cadmium, and further comprising recirculating the organic solvent phase after reextraction to the extraction process. 
     
     
       5. The process according to claim 1, wherein the chlorocomplexes of polyvalent metals are chlorocomplexes of iron(III). 
     
     
       6. The process according to claim 1, wherein the chlorocomplexes of polyvalent metals are chlorocomplexes of zinc(II). 
     
     
       7. The process according to claim 2, wherein the chlorocomplexes used in the aqueous solution during the reextraction are the same as the chlorocomplexes used in the organic solvent phase during the extraction. 
     
     
       8. The process according to claim 1, wherein the amine and ammonium cations, respectively, contain hydrocarbon radicals of 1 to 30 carbon atoms, where said hydrocarbon radicals may have desired chain length values. 
     
     
       9. The process according to claim 8, wherein the number of carbon atoms contained in the hydrocarbon radicals is from 1 to 18 carbon atoms. 
     
     
       10. The process according to claim 8, wherein the hydrocarbon radicals are alkyl radicals, and where at least one of the radicals attached to the nitrogen atom contains at least 6 carbon atoms. 
     
     
       11. The process according to claim 10, wherein the number of carbon atoms contained in one of the radicals attached to the nitrogen atom is at least 8 carbon atoms. 
     
     
       12. The process according to claim 8, wherein the hydrocarbon radicals are aralkyl radicals, and where at least one of the radicals attached to the nitrogen atom contains at least 6 carbon atoms. 
     
     
       13. The process according to claim 12, wherein the number of carbon atoms contained in one of the radicals attached to the nitrogen atom is at least 8 carbon atoms. 
     
     
       14. The process according to claim 2, wherein the acidic aqueous solution for the reextraction of the cadmium ions from the organic phase has a total chloride content of 2 to 58 weight-percent. 
     
     
       15. The process according to claim 14, wherein the total chloride content amounts to 3 to 40 weight-percent. 
     
     
       16. The process according to claim 2, wherein the acidic aqueous solution for the reextraction of the cadmium ions from the organic phase has a content of hydrochloric acid of 2 to 32 weight-percent. 
     
     
       17. The process according to claim 2, wherein the acidic aqueous solution for the reextraction of the cadmium ions from the organic phase has a content of iron ions of 0.01 to 24 weight-percent. 
     
     
       18. The process according to claim 17, wherein the content of iron ions amounts to from 0.05 to 10 weight-percent. 
     
     
       19. The process according to claim 2, wherein the acidic aqueous solution for the reextraction of the cadmium ions from the organic phase has a content of zinc ions of 0.01 to 38 weight-percent. 
     
     
       20. The process according to claim 19, wherein the content of zinc ions amounts to from 0.05 to 10 weight percent. 
     
     
       21. The process according to claim 2, wherein the acidic aqueous solution for the reextraction of the cadmium ions from the organic phase has a content of iron ions and of zinc ions each of 0.01 to 8 weight-percent. 
     
     
       22. The process according to claim 21, wherein the content of iron ions and of zinc ions each amount to from 0.05 to 4 weight-percent. 
     
     
       23. The process according to claim 3, comprising largely removing the free hydrochloric acid, by physical separation methods, from the acidic aqueous solution which is obtained after reextraction and which is enriched with cadmium;   concentrating the remaining solution;   cooling the remaining solution; removing the resulting cadmium-containing precipitate; and   adding the filtrate to the crude phosphoric acid to be subjected to the cadmium removal.   
     
     
       24. The process of claim 23, further comprising recirculating to the extraction stage said removed free hydrochloric acid. 
     
     
       25. The process of claim 23, further comprising recirculating to the reextraction stage said removed free hydrochloric acid. 
     
     
       26. The process according to claim 23, wherein the removal of hydrochloric acid is effected by distillation. 
     
     
       27. The process according to claim 26, wherein 80 to 100 weight-percent of the hydrochloric acid, originally present in the acidic aqueous solution, are removed. 
     
     
       28. The process according to claim 27, wherein the amount of removed hydrochloric acid amounts to 95 to 100 weight-percent. 
     
     
       29. The process according to claim 27, wherein the hydrochloric acid is removed as an azeotropic HCl/H 2  O mixture using a multistage distillation. 
     
     
       30. The process according to claim 27, wherein the hydrochloric acid is removed as an azeotropic HCl/H 2  O mixture using a two-stage distillation. 
     
     
       31. The process according to claim 23, further comprising concentrating the solution remaining after the removal of hydrochloric acid, where a P 2  O 5  -concentration amounts to 40 to 60 weight-percent, and where a concentration of chloride ions can amount to 0.5 to 8.0 weight-percent.   
     
     
       32. The process according to claim 31, wherein the P 2  O 5  -concentration amounts to 45 to 57 weight-percent and wherein the concentration of chloride ions amounts to 1.0 to 6.0 weight-percent. 
     
     
       33. The process according to claim 31, wherein the concentration is carried out in connection with the distillation of HCl. 
     
     
       34. The process according to claim 33, wherein at least part of the distillates of hydrochloric acid and water is recirculated to the extraction and reextraction stage. 
     
     
       35. Process for the removal of cadmium ions from wet process phosphoric acid by liquid-liquid extraction in which the wet process phosphoric acid is contacted with at least one salt present in an organic solvent which is immiscible with water, aqueous salt solutions and aqueous acids which salt is selected from salts of organic primary, secondary and tertiary amines and quaternary ammonium salts, and the organic solvent phase containing the extracted cadmium ions is separated from the wet process phosphoric acid, wherein the above amine and ammonium salts, respectively, are those containing chlorocomplexes of one or more polyvalent metals different from cadmium as anions. 
     
     
       36. The process of claim 35, wherein the extracted cadmium ions present in the separated organic solvent phase are reextracted from the isolated organic phase with an acidic aqueous solution. 
     
     
       37. The process of claim 36, wherein the resulting acidic aqueous reextract solution enriched in cadmium ions is subsequently processed. 
     
     
       38. Process according to claim 36, wherein the acidic aqueous solution used for reextraction contains anionic chlorocomplexes of a polyvalent metal different from cadmium;   wherein the chlorocomplexes of polyvalent metals are a material selected from the group consisting of iron(III) and zinc (II);   wherein the chlorocomplexes used in the aqueous solution during the reextraction are the same as the chlorocomplexes used in the organic solvent phase during the extraction;   wherein a material selected from the group consisting of the amine and ammonium cations contains hydrocarbon radicals of 1 to 30 carbon atoms, which radicals may have desired chain length values; and   wherein the hydrocarbon radicals include a material selected from the group consisting of alkyl and aralkyl radicals, and at least one of the radicals attached to the nitrogen atom contains at least 6 carbon atoms.   
     
     
       39. The process according to claim 38, wherein the number of carbon atoms contained in the hydrocarbon radicals is from 1 to 18 carbon atoms, and wherein the number of carbon atoms contained in the nitrogen atom is at least 8 carbon atoms. 
     
     
       40. The process of claim 38, wherein the organic solvent phase, after reextraction, is recirculated to the extraction process. 
     
     
       41. Process according to claim 36, wherein the acidic aqueous solution for the reextraction of the cadmium ions from the organic phase has a total chloride content of 2 to 58 weight-percent, and wherein the acidic aqueous solution for the reextraction of the cadmium ions from the organic phase has a content of hydrochloric acid of 2 to 32 weight-percent. 
     
     
       42. Process according to claim 41, wherein the acidic aqueous solution has a total chloride content of 3 to 40 weight-percent. 
     
     
       43. Process according to claim 36, wherein from the acidic aqueous solution which is obtained after reextraction and which is enriched with cadmium the free hydrochloric acid is largely removed by physical separation methods, the remaining solution is concentrated, and the resulting cadmium-containing precipitate is removed,   wherein the removal of hydrochloric acid is effected by distillation;   wherein 80 to 100 weight-percent of the hydrochloric acid originally present in the acidic aqueous solution are removed; and   wherein the hydrochloric acid is removed as an azeotropic HCl/H 2  O mixture using a suitably multistage, preferably two-stage, distillation.   
     
     
       44. Process according to claim 43, wherein the acidic aqueous solution for the reextraction of the cadmium ions from the organic phase shows a content of iron ions of 0.01 to 24 weight-percent. 
     
     
       45. Process according to claim 44, wherein the content of iron ions amounts to 0.05 to 10 weight-percent. 
     
     
       46. Process according to claim 43, wherein the acidic aqueous solution for the reextraction of the cadmium ions from the organic phase shows a content of zinc ions of 0.01 to 38 weight-percent. 
     
     
       47. Process according to claim 46, wherein the content of zinc ions amounts to 0.05 to 10 weight-percent. 
     
     
       48. Process according to claim 43, wherein the acidic aqueous solution for the reextraction of the cadmium ions from the organic phase shows a content of iron ions and of zinc ions each of 0.01 to 8 weight-percent. 
     
     
       49. Process according to claim 48, wherein the content of iron ions and of zinc ions each amounts to 0.05 to 4 weight-percent. 
     
     
       50. Process according to claim 43, wherein the amount of the removed hydrochloric acid is 95 to 100 weight-percent. 
     
     
       51. The process of claim 43, wherein the removed free hydrochloric acid is recirculated to the extraction stage. 
     
     
       52. The process of claim 43, wherein the removed free hydrochloric acid is recirculated to the reextraction stage. 
     
     
       53. The process of claim 43, wherein the solution remaining after free hydrochloric acid removal is cooled. 
     
     
       54. The process of claim 43, wherein the filtrate resulting from the removal of said cadmium-containing precipitate is added to the crude phosphoric acid to be subjected to cadmium removal. 
     
     
       55. Process according to claim 43, wherein the solution remaining after the removal of hydrochloric acid is concentrated;   wherein the concentration is carried out in connection with the distillation of HCl; and   wherein at lest part of the distillates is recirculated to the extraction stage.   
     
     
       56. Process according to claim 55, wherein the remaining solution if concentrated to have a P 2  O 5  -concentration of 40 to 60 weight-percent. 
     
     
       57. Process according to claim 56, wherein the remaining solution is to have a P 2  O 5  -concentration of 45 to 57 weight-percent. 
     
     
       58. Process according to claim 55, wherein the remaining solution is to have a concentration of chloride ions of 0.5 to 8.0 weight-percent. 
     
     
       59. Process according to claim 58, wherein the remaining solution is to have a concentration of chloride ions of 1.0 to 6.0 weight-percent. 
     
     
       60. Process according to claim 55, wherein the distillates are hydrochloric acid. 
     
     
       61. Process according to claim 55, wherein the distillates are water. 
     
     
       62. Process according to claim 55, wherein at least part of the distillates is recirculated to the reextraction stage.